NF1X
Nuclear factor 1 X-type (NF1X) is a transcription factor known to bind the palindromic
consensus sequence TTGGC(N)5GCCAA [1], and has been shown to activate replication of
adenoviral DNA [2]. It is highly conserved in vertebrates, with chicken and hamster orthologs
showing 92% amino acid sequence identity [3]. NF1X is reported to control the expression of a
number of different genes in liver [4-8], and is a known repressor of glutathione S-transferase
[9], which is involved in intermediary metabolism of xenobiotics and is also shown to be
rhythmic in our study (additional file 1). NF1 proteins also exhibit a redox-sensitive regulation
of CYP1A transcription in humans [10]. Since CYP1A protein levels alter the oxidative state of
the cell, which in turn activates the transcription of multiple transcription factors [11], CYP1A
could provide a direct link between the pineal clock, cellular redox state, and intermediary
metabolism if the circadian clock regulated it. Future research exploring a redox dependent
regulatory role of NF1X within the chick pineal clock is warranted.
Cystatin C
Cystatin is a potent cysteine protease inhibitor [12] and has been implicated in diverse
processes, including immunomodulation. Chicken cystatin has also been reported to act as a
growth hormone in mouse fibroblasts [12]. The putative role of cystatin in immune function is
intriguing, given that many genes associated with the immune system show circadian
rhythmicity in vivo [13] as well as in vitro (Fig. 2). Furthermore, we hypothesize that cystatin
may interact with redox-sensitive pathways at the posttranslational level, since cysteine thiol
groups are the primary redox-sensing structures.
NDRG1
N-myc downstream regulated 1 (NDRG1) is involved in a wide array of biological
processes, including cellular differentiation and stress responses [14, 15], and is repressed by the
n-myc and c-myc proto-oncogenes. The rhythmic and light inducible expression of NDRG1 may
indicate circadian regulation of n-myc itself. This finding would be of interest since N-MYC
protein activates transcription via binding to E-boxes [16], and subsequently the activation of a
large number of genes involved in ribosomal and protein synthesis [17], consistent with the
result of our functional clustering analysis of pinealocytes in vitro.
Additionally, NDRG1 is reported to be induced by retinoic acid [15] and to associate with
APOLIPOPROTEIN A-I [18].
APOLIPOPROTEIN A-I is a gene product involved in
cholesterol transport which we found to be regulated in a circadian fashion within the chick
pineal (additional file 6). NDRG1 may therefore couple retinoic acid signaling with circadian
regulation of cellular trafficking of lipids in the pineal.
Purpurin
Purpurin belongs to the lipocalin protein family, a diverse group of proteins involved in
various processes including immune function and retinoid binding [19]. Purpurin is known
to be synthesized in retinal photoreceptors [20], and while its function is not fully
understood, it is thought to mediate cellular adhesion and survival [21] as well as having a
role in the transport of retinol within the retina [22]. These properties make purpurin an
interesting potential candidate gene for linking visual input or immune response to the
pinealocyte clock.
REFERENCES
1. Nowock J, Borgmeyer U, Puschel AW, Rupp RA, Sippel AE: The TGGCA protein binds to
the MMTV-LTR, the adenovirus origin of replication, and the BK virus enhancer. Nucleic
Acids Res 1985, 13:2045-2061.
2. Nagata K, Guggenheimer RA, Hurwitz J: Specific binding of a cellular DNA replication
protein to the origin of replication of adenovirus DNA. Proc Natl Acad Sci USA 1983,
80:6177-6181.
3. Kruse U, Oian F, Sippel AE: Identification of a fourth nuclear factor 1 gene in chicken by
cDNA cloning: NF1X Nucleic Acids Res 1991, 19:6641.
4. Anania F, Potter J, Rennie-Tankersley L, Mezey E: Effects of acetaldehyde on nuclear
protein binding to the nuclear factor I consensus sequence in the alpha 2(I) collagen
promoter. Hepatology 1995, 21:1640-1648.
5. Lichtsteiner S, Wuarin J, Schibler U: The interplay of DNA-binding proteins on the
promoter of the mouse albumin gene. Cell 1987, 51:963-973.
6. Garlatti M, Aggerbeck M, Bouguet J, Barouki R: Contribution of a nuclear factor 1 binding
site to the glucocorticoid regulation of the cytosolic aspartate aminotransferase gene
promoter. J Biol Chem 1996, 271:32629-32634.
7. Bois-Joyeux B, Danan JL: Members of the CAAT/enhancer-binding protein, hepatocyte
nuclear factor-1 and nuclear factor-1 families can differentially modulate the activities of
the rat alpha-fetoprotein promoter and enhancer. Biochem J 1994, 301:49-55.
8. Cardinaux JR, Chapel S, Wahli W. Complex organization of CTF/NF-I, C/EBP, and HNF3
binding sites within the promoter of the liver-specific vitellogenin gene. J Biol Chem 1994,
269:32947-32956.
9. Osada S, Ikeda T, Xu M, Nishihara T, Imagawa M: Identification of the transcriptional
repression domain of nuclear factor 1-A. Biochem Biophys Res Commun 1997, 238: 744-747.
10. Morel Y, Barouki R: Down-regulation of cytochrome P450 1A1 gene promoter by
oxidative stress—critical contribution of nuclear factor 1. J Biol Chem 1998, 273: 2696926976.
11. Puga A, Barnes SJ, Chang C, Zhu H, Nephew KP, Khan SA, Shertzer HG: Activation of
Transcription
Factors
Activator
Protein-1
and
Nuclear
Factor-kB
by
2,3,7,8-
Tetrachlorodibenzo-p-dioxin. Biochem Pharm 2000, 59:997-1005.
12. Dickinson DP: Salivary (SD-type) cystatins: over one billion years in the making—but to
what purpose? Crit Rev Oral Biol Med 2002, 13:485-508.
13. Bailey MJ, Beremand PD, Hammer R, Bell-Pedersen D, Thomas TL, Cassone VM:
Transcriptional profiling of the chick pineal gland, a photoreceptive circadian oscillator
and pacemaker. Mol Endocrinol 2003, 17:2084-2095.
14. Agarwala KL, Kokame K, Kata H, Miyata T: Phosphorylation of RTP, an ER stressresponsive cytoplasmic protein. Biochem Biophys Res Commun 2000, 272:641-647.
15. Piquemal D, Joulia P, Balaguer A, Basset A, Marti J, Commes T: Differential expression of
the RTP/Drg1/Ndr1 gene product in proliferating and growth arrested cells. Biochim
Biophys Acta 1999, 1450:364-373.
16. Alex R, Sozeri O, Meyer S, Dildrop R: Determination of the DNA sequence recognized by
the bHLH-zip domain of the N-myc protein. Nucleic Acids Res 1992, 20:2257-2263.
17. Boon K, Caron HN, van Asperen R, Valentijn L, Hermus MC, van Sluis P, Roobeek I, Weis
I, Voute PA, Schwab M, Versteeq R: N-myc enhances the expression of a large set of genes
functioning in ribosome biogenesis and protein synthesis. The EMBO Journal 2001, 20:13831393.
18. Hunter M, Angelicheva D, Tournev I, Ingley E, Chan DC, Watts GF, Kremensky I,
Kalaydjieva L: NDRG1 interacts with APO A-I and A-II and is a functional candidate for
the HDL-C QTL on 8q24. Biochem Biophys Res Commun 2005, 332:982-92.
19. Flower DR: The lipocalin protein family: a role in cell regulation. FEBS Lett 1994, 354:711.
20. Berman P, Gray P, Chen E, Keyser K, Ehrlich D, Karten H, LaCorbiere M, Esch F, Schubert
D: Sequence analysis, cellular localization, and expression of a neuroretina adhesion and
cell survival molecule. Cell 1987, 51:135-142.
21. Schubert D, LaCorbiere M: Isolation of an adhesion-mediating protein from chick neural
retina adherons. J Cell Biol 1985, 101:1071-1077.
22. Schubert D, LaCorbiere M, Esch F: A chick neural retina adhesion and survival molecule
is a retinal-binding protein. J Cell Biol 1986, 102:2295-2301.